POCl3-mediated synthesis of hydrolysis-prone 2-trifluoroethylbenzimidazoles

Loss of a trifluoromethyl group has been observed as an unproductive side reaction in the formation of 2-trifluoroethylbenzimidazoles. A hydrolytic mechanism for this transformation is proposed that is consistent with evidence for the identity of reaction intermediates. Cyclodehydration with POCl3 suppresses hydrolysis of the trifluoromethyl group and provides 2-trifluoroethylbenzimidazoles in good yields.